Tuesday, January 14, 2014

I have a lot of posts in my backlog that have pictures but no text added to them. Since a lot of them are more than one year old I figured I should take the effort to add the text lest I forget what happened.

There is a common problem with the DSO5062B oscilloscopes in that they get a white screen once in a while and require a power cycle to recover, temporarily. The scope seems to be functioning in the mean time but nothing is displayed.

The same device is being sold under many different name and brandings: Tekway DST1062B, Voltcraft DSO5062B, Zhongce, Protek, PCE (like mine) but it's exactly the same thing save for the splash screen and printed logo.

I've bought a cheap broken laptop on eBay for around 20EUR with the description "turns on briefly the fan and the shuts down, no image".

The laptop was actually in pretty good condition, came with a working battery and charger and RAM, but without any hard-drive.

A quick search on the Internet turned up the fact that these laptops usually die from heat, having inadequate cooling on the integrated video card.

I recovered the laptop by using a makeshift heat shield made from a sandwich of aluminium foil and cardboard an using a heatgun (paint stripper) to slowly heat the chip. A blob of leaded solder was used as reflow indicator, knowing that the leadfree solder melts at higher temperatures and the BGA balls take a while to heat up (being under the chip).

A cheap multimeter was used as a temperature indicator, with the thermocouple pressed against the chip body.

The cardboard started smoking after a while but this did not affect the operation in any way. The actual heating process took around 2 minutes, another 30-40 seconds were used to slowly pull the heat gun away from the board and it was left for ambient cooling another 10-15 minutes.

I won't bore you with stories, I think the pictures below tell all the details.

I have been pondering on creating a home network of nodes using cheap slaves and a more powerful master. Since the name did not come up in any Google search I settled upon Node@Home.

My idea is to have gadgets spread around the house/perimeter that can report sensor data to a central station and perform certain actions. It will be first used to start the [electrical] heating remotely, check rooms temperature, actuate the blinds on the outside, log the voltage measured by the home-made PSU, start or unblock the Roomba, etc.

I am sure that with creating an affordable master node (based on Stellaris Launchpad or Raspberry Pi) and disposable slave nodes will make everyone want to have these things around the house.

The minimum requirements for the nodes will be a baseline microcontroller (PIC10/12F, MSP430F, <1$ each) and an NRF24L01 radio transceiver (1-4$). The power of the network will be in the protocol requirements and the software.

UPDATE: the draft below is wrong because I assumed broadcasting was possible with the NRF24 units, which is not. I have written a new one in the mean time but I did not have time to implement a proof-of-concept, so I'm not publishing it until it is proven.However, the payload section will remain mostly as-is.

Here is my first draft for this, loosely based on the BMW IBUS protocol: